Force measuring apparatus including sensitivity selection means

ABSTRACT

Force measuring apparatus of the type including a mechanical oscillator, such as a string, that vibrates under load to produce a signal voltage the frequency of which is a function of the force to be measured. The invention is characterized in that following multiplication of the signal frequency, the signal is fed to multi-stage counter means for selected long or short periods of time corresponding with the desired sensitivity of measurement. The duration of the period of connection is controlled by a gate timing switch which is operable simultaneously with a stage selection switch associated with the counter, whereby when the connection periods are alternately long and short, the signal to be counted is fed to lower and upper counter stages, respectively. The gate tuning switch is operable alternately by a reference signal supplied from a mechanical oscillator, such as a crystal, or a reference string contained in the same housing as the measuring string.

States Patent [1 1 Allenspach et al.

[ 1 FORCE MEASURING APPARATUS INCLUDING SENSITIVITY SELECTION MEANS [75]inventors: Heinz Allenspach, Fallanden; Eugen Meier, Meilen, both ofSwitzerland [73] Assignee: Mettler Instruments AG, Zurich,

Switzerland 221 Filed: Aug. 2, 1972 21 Appl. No.: 277,162

[30] Foreign Application Priority Data [58] Field of Search. 324/78 D,79 D; 73/133, 67.2, 73/137, 138; 235/l5l.33; 177/210, 211, 25

' [451 Jan. 29, 1974 Primary Examiner-Richard B. Wilkinson AssistantExaminer-Vit W. Miska Attorney, Agent, or Firr'nLawrence E. Laubscher 57] ABSTRACT Force measuring apparatus of the type including a mechanicaloscillator, such as a string, that vibrates under load to produce asignal voltage the frequency of which is a function of the force to bemeasured. The invention is characterized in that followingmultiplication of the signal frequency, the signal is fed to multi-stagecounter means for selected long or short periods of time correspondingwith the desired sensitivity of measurement. The duration of the periodof connection is controlled by a gate timing switch which is operablesimultaneously with a stage selection switch associated with thecounter, whereby when the connection periods are alternately long andshort, the

[56 References Cited signal to be counted is fed to lower and uppercounter UNITED STATES PATENTS stages, respectively. The gate tuning swtch is operable alternately by a reference signal supplied from a meat34 3 chanical oscillator, such as a crystal, or a reference 322125O1/1965 324/78 D string contained in the same housing as the measuring2,974,863 3/1961 Williams, Jr. et al 235/157.33 Smng- FOREIGN PATENTS ORAPPLICATIONS 5 Claims 1 D r awing Figure 1,049,595 11/1966 Great Britain324/78 D i 0 13 FREQ.

COUNTER CONTROL f L MEANS s l I REFERENCE:I/ r

| MECHANICAL l l OSCILLATOR I I TARE s STORE S l 11 f5 sToRE 9 PRINTER 185,358

FORCE MEASURING APPARATUS INCLUDING SENSITIVITY SELECTION MEANS Thisinvention relates to a force-measuring apparatus having at least onemechanical oscillator (for example, a measuring string).

Force-measuring devices have been proposed in the prior art that includemechanical oscillator means that are acted upon by the force to bemeasured and whose respective frequency of oscillation is counted over apredetermined measuring period and is used for the digitalrepresentation of the magnitude of the force to be measured. Suchdevices have been put to increasing use (for example, as stringbalances) primarily because of the easy possibility .of digitalrepresentation of the magnitude of force to be measured by frequencycounting (as described in principle, for example, in the journal VDl,volume 98, No.26, pages 1,541 to 1,588, September 1956).

One disadvantage of the previously known devices is that if theresolution and thus the sensitivity of the device are to be increased,it is necessary to provide a prolongation of the measuring time, therebyrequiring more pulses to be counted, which naturally requires more time,for any given frequency of oscillation. This factor sets certain limitson the use of force measuring devices with one or more oscillators,particularly where a rapid sequence of weighing operations combined witha high degree of sensitivity is required. Also, the known devices aregenerally each fixed at a given measuring period due to their design,even for measuring operations in which the advantage of a higher degreeof resolution is of little or no importance and a shorter measuringperiod could therefore advantageously be employed. The latter is alwaysthe case as regards approximate measurements, for example in the case ofbalances for weighing-in operations, for approximate determinations ofweight (for example, in the case of a preliminary determination ofweight), or certain spot checking weighing operations.

Accordingly, a primary object of the present invention is to provide aforce-measuring apparatus including at least one mechanical oscillatorwhich in operation is acted upon by the force to be measured, means forcounting the resulting frequency of oscillation over a givencountingperiod and for representing digitally the magnitude of the forceto be measured, frequency multiplier means for multiplying the frequencyof oscillation of the mechanical oscillator means, and means for varyingthe counting period.

By use of the frequency multiplier means, the number of counting pulsesper unit of time can be of any selected value so that a very substantialsensitivity of display is achieved regardless of the order of magnitudeof the particular frequency of the oscillator. The time involvedtherewith can, if necessary, be reduced by reducing the counting time inany one ofa number of various ways. A preferred arrangement is one inwhich a gate circuit with adjustable gate times and a switchable counterare used. Preferably the gate times are switchable in decade stages.-

One arrangement which has been found desirable for the counter is one inwhich with each reduction in the gate time by one stage, the respectivelowest counting stage is separated off so that the counting pulses passinto the correspondingly higher stages and represent a correspondinglyhigher value of the force. The indication means arranged downstream ofthe counter than always remains correct with regard to place value,which affords advantageous read-off (since in this way an error in theorder of magnitude is scarcely possible, even when switching over to adifferent degree of sensitivity, because the position of the decimalpoint remains uniform).

In accordance with another object of the invention, means are providedfor effecting automatic taring, different oscillator means (for example,a quartz oscillator) being used to supply the reference frequency.Furthermore, with string force-measuring devices it is possible to use areference string of corresponding stability (and preferably identicalgeometry) which is then best arranged in the same housing as themeasuring string, whereby any interference influence, such as changes intemperature, humidity, vibrations, or ageing effects have the sameeffect on the measuring string or strings and on the reference string.

. The various frequencies (oscillator frequency, multiplication factor)and gate times, and also the basic or pre-load of the apparatus, arepreferably so correlated that the counting result will be representeddirectly in units of weight.

One embodiment of the force-measuring apparatus according to the presentinvention will now be described by way of examplev with reference to theaccompanying drawing the single figure of which is a block circuitdiagram of the essential elements of a single-string balance withautomatic taring means.

The string balance, which is generally of the type illustrated in theprior Meier US. application Ser. No. 359,258 filed May'l l, 1973, theGallo U. S. Pat. No. 3,612,198 and the Wirth et al U. S. Pat. No.3,621,713, among others, includes a measuring string Ss which is mountedin a housing H under a preload of 1,700 p, oscillates at a countingfrequency of l5kl-lz. It has a weighing range of p, which produces arise in frequency of string oscillation (signal change) of 500112, whichrepresents for practical purposes a very low degree of resolution.

The particular frequency f, of the measuring string is passed to afrequency multiplier 1 and there increased by 200 times, so that, withthe multipliedcounting frequency rising over the weighingrange, from3,000,000 to 3,100,000 Hz, the signal change represented by the rise instring frequency is now 100,000 Hz.

The multiplied counting frequency is passed to a gate 2 and from there,while the gate is open, to a multistage forward-reverse counter 3.

A reference frequency f, is produced by a quartz oscillator O. Thisfrequency f, is passed to a gate time divider or frequency divider 4,and from there to the gate 2 and also to conventional counter controlmeans 5. The counter control means are of the type disclosed in thecopending Allenspach US. application Ser. No. 244,054 filed Apr. 14,1972, and need not be discussed in detail here. The gate time divider 4can be switched over so as selectively to give a gate open time of 1 sor 0.1 s.

[The gate circuit (gate 2 and divider 4) canalso be controlled by areference string S,- which is preferably arranged in the same housing Has the measuring string Change over is effected by a gate timing switch6 which is operable manually in synchronism with the stage selectionswitch 7,50 that actuation of the switch 6 automatically also actuatesthe switch 7. The stage selection switch 7 has'the effect that, when thegate time is reduced from 1 s to 0.1 s, the counting pulses arrivedisplaced upwardly by a decade stage, (i.e., the place which waspreviously the last place is cut off, thereby reducing the leastsignificant figure by one). i

In this way, even with a reduced counting period, the counting resulthas the correct place values, except that each counting pulse nowrepresents ten times the weight value. For example, instead ofa resultof 85.358 g, the result would be 85.35 g.

After a counting period has elapsed, the resulting condition of thecounter 3 is transferred into indication storage means 8, from which theresult can be read off by an indication means 9. A printer output 10 canalso be provided, as illustrated.

The first place (3) is excepted from the indication, that is to say,with a counting period or gate open time of l s, the result appears insix-figure form, while with a counting period of 0.1 s, it is infive-figure form.

For weighing operations with tare, there is connected in parallel withthe indication storage means 8 a tare storage means 11, whileaforward-reverse logic circuit 12 is also .connected between the countercontrol means 5 and the counter 3. A manually operable tare switch 13 isconnected to the counter control means 5 to act thereon and a Zerodetector 14 is connected to the forward-reverse logic circuit 12. Whencarrying out weighing operations with tare, actuation of the .tareswitch 13 causesthe weight result given by determination of the tare tobe transferred to and stored in the tare storage means 11. In asubsequent weighing operation, the weight value in thetare storage means11 is passed at the beginning of the operation into the counter 3. Theforward-reverse logic circuit 12 causes the counter 3 to countbackwards, that is to say, the counting pulses entering the counter 3are subtracted from the tare weight until the zero detector 14 signalsthat zero weight has been reached in the counter 3. The signal from thezero detector 14 passes to the forwardreverse logic circuit 12 which nowcauses the counter 3 ,to count in the forward direction. In this way,when a gross weighing operation follows determination of the tare, theweighing result given is the net weight.

It is obvious that it is also possible to weigh in a plurality ofcomponents, while indicating the net weight of each component as it isadded, by actuation of the tare switch 13 before each component is to beweighed.

The counter switching-over with correct place values, as describedabove, has the result that a tare value information stored in the means11 at the beginning of a measuring operation is not lost, even after thecounting period has possiblybeen switched over, but retains its correctplace value.

The embodiment described above has two gate times of l s and 0.1 s.Other times could obviously be provided, for example, 2 and 0.2 s, asrequired. Also, instead of two gate times, it is possible to providemore gate times if the particular requirements to which the device issubject make this seem desirable or necessary.

The apparatus according to the invention can also be used as aplus-minus balance. In this case the gate times could, for example, beselected such that one counting pulse corresponds to the permissibleamount of tolerance.

Although the apparatus as described above is in the form of asingle-string measuring apparatus, the invention can also be in the formof a device which utilizes a plurality of controlled measuringoscillators or strings.

The above-described force-measuring apparatus is flexible in use, inthat measurements with a high degree of sensitivity and thus arelatively long measuring time, and measurements with a more moderatedegree of sensitivity and therefore a shorter measuring time, can beselectively performed with the same apparatus. For example, whenweighing-in material, the apparatus can be used to weigh a first amountof added material which is delivered rapidly, weighing being with a lowdegree of sensitivity, until the weight approaches the set value,whereupon the apparatus is switched over to weigh-in a slower additionof material with a higher degree of sensitivity, until the set weight isreached.

What is claimed is:

1. Weighing apparatus, comprising a. means including at least onemechanical oscillator for producing a signal voltage the frequency ofwhich is a function of the force to be measured;

b. frequency multiplier means for multiplying the frequency of saidsignal voltage, thereby to provide a high frequency counting pulsesignal;

0. pulse counter means having first and second stages;

a'. stage selection switch means including a pair of output terminalsconnected with the first and second stages of said counter means,respectively, said stage selection switch means including also an inputterminal; I

e. gate means having an output terminal connected with the inputterminal of said stage selection switch means, said gate means includingan input terminal connected with said frequency multiplier means;

f. means including a reference oscillator and frequency divider meansfor operating said gate means between conductive and non-conductiveconditions in which counting pulses from said frequency multiplier meansare conducted to and isolated from said stage selection switch means,respectively, said frequency divider means including high and lowfrequency output terminals;

g. means including a gate timing switch for varying between two givenlengths the duration of the conductive periods of said gate means, saidgate timing switch being operable between first and second positions toalternately supply said high and low frequency outputs to said gatemeans and to simultaneously switch said stage selection switch meansbetween its first and second positions, respectively, whereby when saidgate timing and stage selection switches are in their first positions,counting pulses for a measurement of one order of sensitivity aresupplied to one stage of said counter means, and when said switches arein their second positions, counting pulses for a measurement of anotherorder of sensitivity are supplied to the other stage of said countermeans; and

h. indicator means connected with said counter means for digitallyrepresenting the magnitude of the loda being measured as a function ofthe instantaneous count of said counter means.

2. Weighing apparatus as defined in claim 1, wherein said mechanicaloscillator includes a vibratory measuring string; and further whereinsaid gate operating means includes a reference string.

3. Apparatus as defined inclaim 2, wherein said frequencies and countingperiods have such a relationship that the counter result is representedby said indicator means in units of weight.

4. Apparatus as defined in claim 2, and further including a housing inwhich both said measuring string and said reference string are mounted.

5. Weighing apparatus, comprising a. at least one mechanical oscillatormeans for producing a signal voltage the frequency of which is afunction of the force to be measured;

b. frequency multiplier means for multiplying the frequency of saidsignal voltage;

c. counter means for counting the number of pulses of said multipliedsignal during a given period of time, said counter means including aforwardreverse counter;

d. indicator means connected with said counter means for digitallyrepresenting the force to be measured as a function of the instantaneouscount of said counter means;

e. means for varying the duration of said counting period, includingnormally non-conductive gate means connected between said frequencymultiplier means and said counter means, and means including a gatetiming switch for rendering conductive said gate means for relativelylong and relatively short conductive periods, respectively; and f.taring means comprising 1. tare store means for storing an initial tarecount; 2. forward-reverse logic means controlling the direction ofoperation of said counter means;

3. counter control means connected with said tare net weight.

1. Weighing apparatus, comprising a. means including at least onemechanical oscillator for producing a signal voltage the frequency ofwhich is a function of the force to be measured; b. frequency multipliermeans for multiplying the frequency of said signal voltage, thereby toprovide a high frequency counting pulse signal; c. pulse counter meanshaving first and second stages; d. stage selection switch meansincluding a pair of output terminals connected with the first and secondstages of said counter means, respectively, said stage selection switchmeans including also an input terminal; e. gate means having an outputterminal connected with the input terminal of said stage selectionswitch means, said gate means including an input terminal connected withsaid frequency multiplier means; f. means including a referenceoscillator and frequency divider means for operating said gate meansbetween conductive and nonconductive conditions in which counting pulsesfrom said frequency multiplier means are conducted to and isolated fromsaid stage selection switch means, respectively, said frequency dividermeans including high and low frequency output terminals; g. meansincluding a gate timing switch for varying between two given lengths theduration of the conductive periods of said gate means, said gate timingswitch being operable between first and second positions to alternatelysupply said high and low frequency outputs to said gate means and tosimultaneously switch said stage selection switch means between itsfirst and second positions, respectively, whereby when said gate timingand stage selection switches are in their first positions, countingpulses for a measurement of one order of sensitivity are supplied to onestage of said counter means, and when said switches are in their secondpositions, counting pulses for a measurement of another order ofsensitivity are supplied to the other stage of said counter means; andh. indicator means connected with said counter means for digitallyrepresenting the magnitude of the loda being measured as a function ofthe instantaneous count of said counter means.
 2. Weighing apparatus asdefined in claim 1, wherein said mechanical oscillator includes avibratory measuring string; and further wherein said gate operatingmeans includes a reference string.
 2. forward-reverse logic meanscontrolling the direction of operation of said counter means;
 3. countercontrol means connected with said tare store means and said logic meansfor transferring to said counter means the count stored in said tarestore means, said logic means being operable to initially cause thecounter means to count in the reverse direction the pulses to bemeasured; and
 3. Apparatus as defined in claim 2, wherein saidfrequencies and counting periods have such a relationship that thecounter result is represented by said indicator means in units ofweight.
 4. Apparatus as defined in claim 2, and further including ahousing in which both said measuring string and said reference stringare mounted.
 4. zero detector means connected with said logic means forreversing the direction of said counter means when the count thereofequals zero, whereby when a gross weighing operation follows adetermination of tare, the weighing result is the net weight. 5.Weighing apparatus, comprising a. at least one mechanical oscillatormeans for producing a signal voltage the frequency of which is afunction of the force to be measured; b. FREQUENCY multiplier means formultiplying the frequency of said signal voltage; c. counter means forcounting the number of pulses of said multiplied signal during a givenperiod of time, said counter means including a forward-reverse counter;d. indicator means connected with said counter means for digitallyrepresenting the force to be measured as a function of the instantaneouscount of said counter means; e. means for varying the duration of saidcounting period, including normally non-conductive gate means connectedbetween said frequency multiplier means and said counter means, andmeans including a gate timing switch for rendering conductive said gatemeans for relatively long and relatively short conductive periods,respectively; and f. taring means comprising